How can I go back to the original interface layout?
Save and close your file, fully close Blender and then open a new Blender instance with the correct default layout.

Then go to File > Open and browse to open your desired file, but before you open uncheck the Load UI option on the bottom left of the File Browser window.

If when you open Blender by default the layout is already messed up you may have to delete your Startup.blend file from the user preferences folder either under


Blender/2.##/config for portable installations or under 
or %APPDATA%\Blender Foundation\Blender\2.##\config for formal installation, generally under C:\Users\&lt;UserName&gt;\AppData\Roaming\Blender Foundation\Blender\&lt;VersionNumber&gt;\config for Windows users